One of the problems with prior art expansion tools is that the tubular expander itself is frequently housed within an outer tubular housing which inherently has a diameter greater than the diameter of the expander. Accordingly, it is frequently difficult to position this housing with the internal expander therein at the desired location at the lower end of the tubular in a well, particularly when there is a substantial variance between the OD of the tubular expander housing and the OD of the tubular prior to being expanded.
A further significant problem with conventional tubular expander techniques is that axial movement of the tubular expander must be stopped before reaching the upper end of the tubular being expanded, since an expander under high force will tend to “shoot past” the upper end of the tubular during the expansion process, thereby resulting in an unsafe condition. Accordingly, operators typically stop upward progress of the expander before the upper end of the casing being expanded, then lower the expander in the well, then use a cutting tool to separate the uppermost portion of the tubular string which is not expanded from the portion of the tubular string which is expanded. Once the expander is removed from the well, the cut-off upper portion of the tubular string may be similarly removed from the well.
Various hydraulic expansion tools and methods have been proposed for expanding tubular while downhole. While some of these tools have met with success, a significant disadvantage to these tools is that, if a tool is unable to continue its expansion operation (whether due to the characteristics of a hard formation about the tubular, failure of one or more tool components, or otherwise), it is difficult and expensive to (a) retrieve the tool to the surface to repair the tool, (b) utilize a more powerful tool from the beginning to continue the downhole tubular expansion operation, or (c) sidetrack around the stuck expander. Accordingly, techniques have been developed to expand a downhole tubular from the top down, rather than from the bottom up, so that the tool may be more easily retrieved.
U.S. Pat. No. 5,348,095 discloses a method of expanding a casing downhole utilizing a hydraulic expansion tool. U.S. Pat. No. 6,021,850 discloses a downhole tool for expanding one tubular against either a larger tubular or the borehole. Publication U.S. 2001/0020532 A1 discloses a tool for hanging a liner by pipe expansion. U.S. Pat. No. 6,050,341 discloses a running tool which creates a flow restriction and a retaining member moveable to a retracted position to release upon the application of fluid pressure. U.S. Pat. No. 6,250,385 discloses an overlapping expandable liner. A high expansion diameter packer is disclosed in U.S. Pat. No. 6,041,858. U.S. Pat. No. 5,333,692 discloses seals to seal the annulus between a small diameter and a large diameter tubular.
The disadvantages of the prior art are overcome by the present invention, and an improved tool and technique are hereafter disclosed for expanding a downhole tubular.